Cataract surgery is the most commonly performed operation in the United States. The term "cataract" refers to a condition in which the normally clear lens in the eye loses its clarity thereby producing visual loss. Recent advances in cataract surgery have allowed removal of the opacified lens through a small incision and replacement of the lens by a manufactured artificial lens or intraocular lens implant.
Typically, the ophthalmic surgeon makes one or two small (1.0-1.5 mm.) incisions initially into the eye to allow placement of small diameter surgical instruments or cannulas. These instruments allow the surgeon to perform an unroofing of the outer covering of the lens (lens capsule).
This procedure (capsulotomy) is effected under a protective gel (viscoelastic) which prevents the front of the eye or anterior chamber from collapsing.
After the conjunctiva is dissected with scissors, to dimensions allowing creation of a scleral incision of measured length and depth, hemostasis is obtained with a cautery or diathermy device. A scleral incision is then made after the conjunctiva has been recessed in order to allow access to the sclera. The sclera is dissected with a dissecting blade into the limbal are allowing entry of a small knife blade (1.0-1.5 mm diameter)
This initial incision must then be enlarged (3.0-3.2 mm.) to accommodate the placement of an instrument to remove the lens. The incision is once again enlarged (4.0-7.0 mm.) to allow insertion of the intraocular lens (IOL) within the original lens capsule. The viscoelastic is then removed and the sclera sutured to complete the procedure.
The procedure of cataract surgery is commonly performed with sterile, disposable scalpel blades to minimize the likelihood of infection.
Heretofore, scalpels of specific, standardized sizes and shapes were utilized in cataract surgery for each phase of the operation. The scalpel blades have been formed with many variations in shape, size and nomenclature. The type of blade commonly used for piercing the cornea and entering the anterior chamber is called a keratome. Keratomes of various profiles are known, each of which produces a measured, standardized incisional width. The cataract surgical procedure requires keratomes of different sizes to produce a measured incision. Alternatively, rulers or calipers which measure the length of an incision, may be used along with scissors or non-calibrated scalpels in order to enlarge an incision. The use of multiple, differently configured scalpel blades for different phases of the surgical procedure is costly. It requires that the surgeon change instruments when proceeding from one phase of the incision-making procedure to the next.
In one conventional embodiment of a piercing blade, a "needle-knife" (after Ziegler) is used to penetrate the cornea. Other lancet blades exist under the names of various manufacturers. One such embodiment is a "V-Lance" manufactured by Alcon Ophthalmic which comprises a honed tip which is tapered and affixed by a metal shaft to a plastic handle. The dimensions of the blade allow entry into the cornea for producing a small (1.5 mm ) incision which is beveled and self sealing. These blades are not useful for enlarging incisions because they are not sufficiently sturdy. They also require measuring devices to determine the width of the incision.
In another embodiment known as a "#57 Beaver Blade", a tapered, honed "hockey stick" shaped blade is used to dissect scleral tissues with sterile, disposable blades and reusable, sterilizable handles. This blade is not useful for initiating a corneal incision or for enlarging it since it requires the use of a ruler or caliper. It is too blunt to make a precise piercing incision.
In another embodiment, a "Guardian Scalpel" manufactured by Myocure, allows scleral incisions employing a plastic sleeve whereby penetration to a precise depth is assured. However, it is not sufficiently precise for enlarging an incision beyond its initial width without a caliper or ruler. It is not useful for dissection of a scleral pocket.
In another embodiment, a blade manufactured from a sliver of diamond attached to an autoclavable holder with or without a micrometer attachment is used to produce incisions of proper depth. These "diamond knives" are of fixed width but adjustable depth. These blades are not disposable and are quite expensive. They are subject to breakage if not handled with great care. A caliper or measuring device is similarly required to enlarge an incision.
In another embodiment, a "Phako-Keratome" produces incisions into the anterior chamber after a scleral flap of tissue or scleral pocket is dissected. This blade produces an incision of specific width and is disposable, sterile and can be placed on a single use or reusable handle. The fixed width of this blade is accurate only for the initial incision. A ruler or caliper must be used to measure the length of incisions being enlarged with this instrument. It is not useful for dissecting scleral flaps.
The evolution of small incision surgery was developed with refinements in the procedure over many years. A few years ago cost containment in these procedures was not a major factor since the cost of such procedures and of disposable blades were reimbursed by third party payers. In the present era of escalating costs for health care, with decreasing reimbursements, the need for reducing the cost of disposable items, i.e. blades and instruments has become a factor in seeking the design of a multi-purpose blade. In the current state of the art, the blades are of single use and disposable and different blades are required for each phase of the cataract procedure.
Recent advances in cataract surgery have made it possible to implant intraocular lenses through small incisions. This requires that a scleral flap or pocket be dissected in order to allow the incision to be self sealing, or require a minimum number of sutures.
A scleral groove is formed in the sclera, at a measured distance from, and parallel to, the corneal limbus. The depth of the scleral incision is usually estimated by the surgeon The sclera is only 0.6 mm. in thickness at the limbus of the eye and may vary in thickness in some patients with ocular disease. If a surgeon wishes to make a 200 micron or 400 micron deep scleral groove prior to fashioning a scleral flap or pocket, a simple method of gaging the depth of this groove is desirable. Some scalpel blades have guards on them in order to prevent making this groove too deep (Myocure). Some use a micrometer attached to a guarded scalpel to allow continual adjustment of the incisional depth (diamond knives).
A simple, visually apparent method of performing this task (while not requiring that the scalpel be removed from the incision) to measure the depth of the groove would be advantageous.
Presently, blades with guards are the only way to judge the depth of an incision accurately. A blade which provides this feature without the use of a guard would be very desirable.
The groove is then dissected toward the limbus until the anterior aspect of the limbus is reached maintaining a constant scleral thickness and forming a "pocket". These scleral pocket-type incisions require a blade of tapering edge thickness in order to allow gradual and controlled incisions. The desired distance from the limbus of this initial groove may vary from one surgeon to another. Some surgeons place incisions anteriorly at the imbus, some posteriorly. The distance from the limbus in a posterior scleral pocket incision may range from 1.0-4.0 mm. A caliper, ruler or other measuring device is required to determine and verify its location.
A scalpel blade which could make this incision and act as its own "visual" caliper would obviate the need for an assistant to measure the distance from the limbus (sometimes repeated measurements are required). The surgeon's ability to monitor the length of the incision while placing the incision would help to expedite the performance of the procedure.
Once the scleral groove is complete, the "pocket" is fashioned by the dissecting blade. A planar dissection is made by using the dissecting blade to "tunnel" a pocket of measured depth into the sclera.
Presently, guarded scalpels require that the guard be removed in order to perform this "tunnelling" maneuver. A blade which uses no guard but provides the capability of forming a pocket of measured depth would be greatly beneficial.
An entry into the anterior chamber through the cornea is made to allow bimanual manipulation of the cataractous lens. A separate 1.0-1.5 mm. wide blade of tapered dimensions and of approximately 1.0 mm length is usually used. The scleral pocket is then entered with a keratome of 3.0-3.2 mm. This allows the use of a cannula which infuses a viscoelastic gel. The gel is instilled in order to allow the central anterior lens surface to be removed in a controlled manner (capsulotomy), without loss of anterior chamber depth.
A lens removal device such as a phakoemulsifier, etc. is then introduced through this measured incision. After the lens is removed, a scissors or a keratome is used to enlarge the incision. If a scissors is used, this requires that a caliper or ruler be employed. If a keratome is used initially, a second keratome of larger size is used at this time to enlarge the incision to accommodate the diameter of a lens implant of the required size.
Each of the incisions and the procedure of lengthening the scleral pocket has heretofore required the use of several different disposable scalpel blades of specific size. This increases the cost of performing the procedure, as well as requiring the changing of blades.